I have asked that question here myself. I believe they were indeed involved in this. I don’t believe Steele is a retired agent. He may very well be an active agent.
Given that there really isn’t any such thing as an ex-spy, my money is on the UK government having had a key role in this affair and that any conversation we have with them in the future ought to be about what they can do to convince us not to nuke London in retaliation.